Methacrylic-based resins represented by methyl polymethacrylate (PMMA) have high transparency, and are hence widely used in fields such as optical materials, vehicle parts, construction materials, lenses, housewares, OA devices, and lighting equipment.
Among these fields, in the field of covers used for vehicle parts, from the perspectives of scratch resistance and transparency, methacrylic-based resins are frequently used.
Recently, among vehicle parts to be mounted in a vehicle, vehicle interior parts have been increasingly installed in positions that tend to be exposed to direct sunlight from the perspectives of design of the vehicle interior, visibility of the instruments, and the like. Such vehicle interior parts tend to be subjected to high-temperature conditions more often than before, and need to have higher heat resistance.
Further, among vehicle parts, even for vehicle exterior parts applications, such as tail lamps and vehicle lamps, there is a need to reduce the thickness of the molded pieces to reduce weight. However, the heat resistance of conventional methacrylic-based resins is insufficient, and distortion can occur when exposed to high-temperature conditions unless the part has a certain thickness. Therefore, there is a need for a methacrylic-based resin with higher heat resistance than that of conventional ones.
In addition, among vehicle parts such as those described above, there are parts requiring transparency, such as an instrument cover and a tail lamp cover, which are required to allow a driver wearing polarized sunglasses to see through so that such driver can see the inside thereof.
When a resin having high birefringence is used as a material for such a part, it may be difficult to see inside through the part due to moire patterns resulting from distortion that was produced during molding.
To solve problems relating to visibility such as those described above, one option may be to increase the molding temperature so as to reduce molding distortion. However, the material needs to have even higher thermal stability.
In view of the above-described conventional situation, there are cases in which, from the perspective of heat resistance, a polycarbonate resin is used for the material of a vehicle part cover. However, since polycarbonate resins have poor scratch resistance and weatherability, a hard coat needs to be applied to the surface to impart scratch resistance and weatherability. As a result, there are the problems of limitations in the shape and an increase in costs.
In response to such problems, a resin having a methyl methacrylate homopolymer, for example, as a main component has been proposed as an acrylic-based resin having improved heat resistance (e.g., refer to Patent Literature 1). Further, a tail lamp lens that uses a maleic anhydride copolymer has been proposed (e.g., refer to Patent Literature 2).